Novel thermosetting resins and process for preparing the same comprising reacting a novolak with a titanic acid ester

ABSTRACT

A novel thermosetting resin, the thermoset resin obtained therefrom having such a thermal resistance that the temperature at which the thermoset resin is caused to show a weight loss of 6% by heating at a temperature elevation rate of 10°C. per minute is at least 400°C., is prepared by reacting a specific phenolic resin with a member selected from the group consisting of a silicic acid ester of the formula Si(OR) 4  wherein R represents alkyl or aryl, a titanic acid ester of the formula Ti(OR) 4  wherein R has the same meaning as defined above and a mixture thereof in the presence of an alkaline catalyst while keeping the reaction system in a molten state, to an extent that 20 - 70 mole %, based on the phenol present in the starting system to be reacted with said member, of phenolic hydroxyl groups in terms of the amount of phenol, remain unreacted. The thus obtained novel resins of the present invention can be easily set or hardened in accordance with the ordinary manner; namely by mixing with a thermohardening agent such as hexamethylenetetramine and then heating, to give thermoset resins having a superior thermal resistance as compared with the conventional phenolic resins. In addition, the thermoset resins obtained from the novel resins of this invention are excellent in mechanical strength, electrical properties and luster of molded articles.

This invention relates to novel thermosetting resins and a process forpreparing the same.

More particularly, this invention relates to a novel thermosetting resinpossessing a superior property in respect of thermal resistance and aprocess for preparing the same.

In recent years there has increased a demand for heat-resistant plasticmaterials to be used for the industrial purposes and many attempts havebeen made to develop such heat-resistant plastic materials. In fact,although there is an increasing use requiring high heat-resistance ofthe various molded articles, there have rarely been found thermosettingresins, particularly phenolic resins, which are resistant to temperatureas high as more than 400°C. It is well known that the thermal stabilityof conventional phenol-formaldehyde resisns is insufficient for thevarious uses since the methylene bridges tend to be thermally decomposedat relatively high temperature.

For the purpose of developing thermosetting resins possessing a superiorproperty in respect of thermal resistance, we have made intensivestudies, particularly, on phenolic resins. As a result, it has beenunexpectedly found that a phenolic resin is reacted with a memberselected from the group consisting of a silicic acid ester, a titanicacid ester and a mixture thereof to have oxygens of the phenolichydroxyl groups of the phenolic resin bonded directly to silicon,titanium or a mixture thereof whereby the thermal stability of theresulting resin can be greatly improved.

It is, accordingly, an object of the present invention to provide athermosetting resin the thermoset resin obtained from which is superiorin thermal resistance.

It is another object of the present invention to provide a process forthe preparation of a thermosetting resin of the character described,which is simple in operation and commercially useful.

The foregoing and other objects, features and advantages of thisinvention will become apparent to those skilled in the art from thefollowing detailed description.

Essentially, according to the present invention, there is provided athermosetting resin, the thermoset resin obtained therefrom having sucha thermal resistance that the temperature at which the thermoset resinis caused to show a weight loss of 6% by heating at a temperatureelevation rate of 10°C. per minute is at least 400°C., which comprises areaction product of a novolak which is obtained by the reaction of aphenol and an aldehyde in the presence of an acid catalyst or a phenolicresin which is obtained by the reaction of a phenol and an aromatichydrocarbon-aldehyde condensation initial-stage reaction product with amember selected from the group consisting of a silicic acid ester of theformula Si(OR)₄ wherein R represents alkyl or aryl, a titanic acid esterof the formula Ti(OR)₄ wherein R has the same meaning as defined aboveand a mixture thereof, said reaction product having such structure thatthe silicon, titanium or a mixture thereof is bonded directly to oxygensof the phenolic hydroxyl groups while 20 - 70 mole %, based on thephenol present in the starting system to be reacted with said member, ofthe phenolic hydroxyl groups, in terms of the amount of phenol, are leftin the free form. Such novel thermosetting resin can be prepared byreacting a novolak which is obtained by the reaction of a phenol and analdehyde in the presence of an acid catalyst or a phenolic resin whichis obtained by the reaction of a phenol and an aromatichydrocabon-aldehyde condensation initial-stage reaction product with amember selected from the group consisting of a silicic acid ester of theformula Si(OR)₄ wherein R represents alkyl or aryl, a titanic acid esterof the formula Ti(OR)₄ wherein R has the same meaning as defined aboveand a mixture thereof in the presence of an alkaline catalyst whilekeeping the reaction system in a molten state, to an extent that 20 - 70mole %, based on the phenol present in the starting system to be reactedwith said member, of phenolic hydroxyl groups, in terms of the amount ofphenol, remain unreacted.

The phenolic condensation initial-stage reaction product to be employedas a starting material in the process of the present invention; namely,a novolak or a phenolic resin consisting of a reaction product of aphenol and an aromatic hydrocarbon-aldehyde condensation intial-stagereaction product, is a known product and can readily be prepared inaccordance with the orinary method. Thus, illustratively stated,according to the process of this invention, a phenol is reacted with analdehyde of an amount of 0.7 - 1.0 moles, preferably 0.75 - 0.9 molesper mole of the phenol at a temperature of 80°- 150°C. in the presenceof an acid catalyst for 10 - 250 minutes to form a novolak having adesired degree of condensation, followed by removal of the aldehyderemaining unreacted and the water produced during the reaction underreduced pressure, an alkaline catalyst is added to render the reactionsystem alkaline and then a silicic acid ester, a titanic acid ester or amixture thereof is added to allow the reaction to proceed, while keepingthe reaction system in a molten state, to an extent that 20 - 70 mole %,based on the phenol present in the starting system to be reacted withsaid ester, of phenolic hydroxyl groups, in terms of the amount ofphenol, remain unreacted. In case an aromatic hydrocarbon-aldehydecondensation initial-stage reaction product is employed, a phenol isreacted with the aromatic hydrocarbon-aldehyde condensationinitial-stage product of an amount of 1 - 2 parts by weight, preferably1.1 - 1.3 parts by weight per part by weight of the phenol in thepresence of a strong acid catalyst, such as sulfuric acid,benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid or thelike at a temperature of 80°- 200°C. for 30 - 30. minutes followed byremoval of water under reduced pressure and an alkaline catalyst isadded to render the reaction system alkaline, whereupon a silicic acidester, a titanic acid ester or a mixture thereof is added to allow thereaction to proceed, while keeping the reaction system in a moltenstate, to an extent that 20 - 70 mole %, based on the phenol present inthe starting system to be reacted with said ester, of phenolic hydroxylgroups, in terms of the amount of phenol, remain unreacted.

The term "a phenol" used herein is intended to mean a monohydric phenolsuch as phenol (monohydroxybenzene), cresol or the like; a polyhydricphenol such as 2,2-bis(p-hydroxyphenyl)- propane(bisphenol A),2,6-bis(2-hydroxybenzyl) phenol or the like; or a mixture thereof.

The term "aldehyde" used herein is intended to mean an aldehyde capableof forming a phenolic resin in cooperation with a phenol, for exampleformaldehyde, acetaldehyde, furfural or the like.

The aromatic hydrocarbon-aldehyde condensation initial-stage reactionproducts to be employed in the process of this invention are suitablythose having an average molecular weight of 250 - 1,000 and includeresins obtained by condensation reaction of an aldehyde with xylene,toluene, acenaphthene, cymene, mesitylene, 1,2,4-trimethylbenzene,durene, naphthalene, pentamethylbenzene, acenaphthylene and the like.

Examples of the silicic acid esters to be employed in this inventioninclude tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane,tetrabuthoxysilane, tetraphenoxysilane and tetrabenziloxysilane, whichmay be employed alone or in mixture thereof. Examples of the titanicacid esters to be employed in this invention include titaniumtetraisopropoxide, titanium tetrabuthoxide, tetra(2-ethyl)hexyltitanate, tetrastearyl titanate, titanyl acetylacetonato and titaniumtetraphenoxide, which may be employed alone or in mixture.

In carrying out the process of the present invention, it is ofimportance to terminate the reaction so that 20 - 70 mole %, based onthe phenol present in the starting to be reacted with the ester, of thephenolic hydroxyl groups, in terms of the amount of phenol, may remainunreacted. It is achieved by controlling the amount of the esteremployed. Illustratively stated, while the silicic acid esters and thetitanic acid esters may also be employed in mixture thereof, the silicicacid ester and/or the titanic acid ester may be employed in an amount of0.06 - 0.2 molar equivalents, based on the amount of phenol or phenolicvalue in the starting system to be reacted with the ester.

The reaction is effected while keeping the reaction system in a moltenstate but attention should be given so that the reaction temperature iskept below the boiling point of the silicic acid ester or the titanicacid ester employed. The reaction time is not critical but is usually20 - 150 minutes for which substantially all of the silicic acid esterand/or the titanic acid ester employed is reacted with phenol componentpresent in the starting system. The reaction is carried out in thepresence of an alkaline catalyst. Examples of suitable alkalinecatalysts include alkali and alkaline earth metal hydroxide such aspotassium hydroxide, sodium hydroxide, lithium hydroxide, calciumhydroxide, barium hydroxide, strontium hydroxide and magnesiumhydroxide; primary amines such as methylamine, ethylamine, propylamineand butylamine; secondary amines such as ethylenediamine anddiethylamine; and tertiary amines such as triethanolamine. The reactionsystem is maintained at an alkaline condition, preferably at a pH valueof 7.5 - 10.0.

As described hereinbefore, the present invention has been made, based onsuch novel finding that if, partly in substitution for hydrogen of thephenolic hydroxyl groups of the novolak or the phenolic resin from aphenol and an aromatic hydrocarbon-aldehyde condensation initial-stagereaction product, silicon and/or titanium is bonded to oxygens of saidphenolic hydroxyl groups, the resulting phenolic resin is imparted asuperior property in respect of the thermal resistance, that is, thethermoset resin obtained such resulting phenolic resin has suchexcellent thermal resistance that the temperature at which the thermosetresin is caused to show a weight loss of 6% by heating at a temperatureelevation rate of 10°C. per minute is at least 400°C. Differentlystated, the thermosetting resins of the present invention have anentirely novel structure. For explaining this feature of this inventionmore clearly, the reaction formula in the process according to thisinvention is given below, taking as an example the case where typicalmaterials are employed. ##SPC1##

wherein n is 3 - 10 in average. As apparent from the above, theincorporation of silicon and/or titanium bonded to oxygens of thephenolic hydroxyl groups into the structure of resin is essential to thepresent invention. Such incorporation of silicon and/or titanium iseffected with expulsion of the corresponding alcohol to the ester used.Accordingly, the kinds of classes of the alkyl or aryl have nosignificance in the present invention.

The thus obtained novel resins of the present invention can be easilyset or hardened in accordance with the ordinary manner; namely by mixingwith a thermohardening agent such as hexamethylenetetramine (hexamine),polyoxymethylene or the like and then heating, to give thermoset resinshaving a superior thermal resistance as compared with the conventionalphenolic resins. In addition, the thermoset resins obtained from thenovel resins of this invention are excellent in mechanical strength,electrical properties and luster of molded articles. Particularly, whenxylene-formaldehyde resin is employed as an aromatichydrocarbon-aldehyde resin in this invention, the resulting resin has anexcellent property in respect of adhesiveness to metals.

The following examples are given only for the purpose of illustratingthis invention.

EXAMPLE 1

245 g. of phenol (monohydroxybenzene) and 165 g. of formalin(formaldehyde content: 37% by weight. The same is referred to thefollowing examples) were charged in a four-neck flask and 2 ml. of 1NHCl were then added while stirring. The reaction was allowed to proceedat 100°C. for 90 minutes, followed by removal of water under reducedpressure. To the resulting reaction mixture 8 ml. of a 10% aqueoussolution of potassium hydroxide were added at 100°C., immediatelywhereupon 54 g. of tetraethoxysilane were added and heated to 130°C. Thereaction was allowed to proceed for 100 minutes and then the reactionmixture was concentrated to give a white, solid resin. To the thusobtained resin were added 10% by weight of hexamine and heated at 170°C.to obtain an infusible product, the thermal resistance of which is givenin Table 1 (shown later).

EXAMPLE 2

In the substantially same manner as described in Example 1, 94 g. ofphenol, 82 g. of bisphenol A and 65 g. of formalin were charged in aflask and molten, with stirring, by heating. 1 Ml of 1N HCl were addedat 100°C. for 30 minutes, followed by removal of water under reducedpressure. Then, 6 ml. of a 10% aqueous solution of potassium hydroxidewere added at 100°C., immediately whereupon 30 g. of tetraethoxysilanewere added and heated to 145°C. The reaction was allowed to proceed for120 minutes followed by concentration under reduced pressure to give awhite, solid resin. The resin was hardened by mixing with 10% by weightof hexamine and heating. The thermal resistance of the thermohardenedresin is given in Table 1.

EXAMPLE 3

In the substantially same manner as described in Example 1, 100 g. ofNikanol H (trade name of xylene-formaldehyde resin manufactured and soldby Nihon Gasu Kagaku Kabushiki Kaisha, Japan and having an averagemolecular weight of 350 - 500 and a viscosity [η]20°C of 3,000 -100,000) and 130 g. of phenol were charged in a flask and 1.5 ml. ofbenzenesulfonic acid (purity: 80%) were added, whereupon the reactionwas allowed to proceed at 95°C. for 100 minutes, followed by removal ofwater. Then, 8 ml. of a 10% aqueous solution of potassium hydroxide at105°C. and subsequently 34.5 g. of tetraethoxysilane were added. Thereaction system was heated to 130°C. and the reaction was allowed toproceed for 100 minutes, followed by concentration to give a white,solid resin. The thus obtained resin could easily be hardened byheat-treatment using 10% by weight of hexamine. The thermal property isshown in Table 1.

EXAMPLE 4

In the substantially same manner as described in Example 1, 100 g. ofthe Nikanol H and 130 g. of phenol were charged in a flask, whereupon1.5 g. of ptoluene-sulfonic acid were added. The reaction was allowed toproceed at 95°C. for 100 minutes, whereupon 5 ml. of a 10% aqueoussolution of potassium hydroxide to render the reaction system weaklyalkaline. Then, 23 g. of formalin were added to allow the reaction toproceed for 30 minutes, followed by removal of water under reducedpressure. When the temperature was elevated to 105°C., 3 ml. of a 10%aqueous solution of potassium hydroxide were added and then 34.5 g. oftetraethoxysilane were added. The reaction system was heated to 130°C.to allow the reaction to proceed for 100 minutes, followed byconcentration to give a white, solid resin. The thus obtained resin washardened with a comparatively high velocity by heat-treatment using 10%by weight of hexamine. The thermal property is shown in Table 1.

EXAMPLE 5

245 g. of phenol and 165 g. of formalin were charged in a four-neckflask and 2 ml. of 1N HCl were added with stirring, whereupon thereaction was allowed to proceed at 95°C. for 100 minutes, followed byremoval of water under reduced pressure. When the temperature of thereaction system was elevated to 95°C., 8 ml. of an aqueous solution ofpotassium hydroxide were added. Immediately after the addition of saidaqueous solution, 64 g. of titanium tetraisopropoxide and the reactionwas allowed to proceed at 95°C. for 100 minutes, followed byconcentration to give a red, solid resin. The resin was hardened byheat-treatment using 10% by weight of hexamine. The thermal property ofthe thus obtained thermohardened resin is shown in Table 1.

EXAMPLE 6

In the substantially same manner as described in Example 5, 94 g. ofphenol, 82 g. of bisphenol A and 65 g. of formalin were mixed and moltenby heating. Then, 1 ml. of 1N HCl was added and the reaction was allowedto proceed at 95°C. for 30 minutes, followed by removal of water underreduced pressure. To the reaction mixture were added, at 95°C., 6 ml. ofa 10% aqueous solution of potassium hydroxide, immediately after which45 g. of titanium tetraisopropoxide were added and the reaction wasallowed to proceed for 120 minutes, followed by concentration underreduced pressure to give a red, solid resin. The resin was hardened bymixing with 10% by weight of hexamine and heating. The thermal propertyof thus obtained thermoset resin is shown in Table 1.

EXAMPLE 7

In the substantially same manner as described in Example 5, 100 g. ofNikanol H and 130 g. of phenol were charged in a four-neck flask and 1.5ml. of benzenesulfonic acid were added with stirring, whereupon thereaction was allowed to proceed at 95°C. for 120 minutes, followed byremoval of water. At 95°C. 8 ml. of a 10% aqueous solution of potassiumhydroxide were added to the system and 34.5 g. of titaniumtetraisopropoxide were added, whereupon the reaction was allowed toproceed for 100 minutes, followed by concentration under reducedpressure to give a red, solid resin. The resin was hardened byheat-treatment using 10% by weight of hexamine. The thermal property ofthe thus obtained thermoset resin is shown in Table 1.

EXAMPLE 8

In the substantially same manner as described in Example 7, 100 g. ofNikanol H and 130 g. of phenol were mixed and 1.5 g. ofp-toluenesulfonic acid were added, whereupon the reaction was allowed toproceed at 95°C. for 90 minutes. Then, 5 ml. of a 10% aqueous solutionof potassium hydroxide were added to render the reaction system weaklyalkaline and 23 g. of formalin were added, whereupon the reaction wasconducted for 30 minutes, followed by removal of water. At 95°C. 3 ml.of a 10% aqueous solution of potassium hydroxide were added to thesystem and then 34.5 g. of titanium tetraisopropoxide were added,whereupon the reaction was allowed to proceed for 100 minutes to give ared, solid resin. The resin was mixed with 10% by weight of hexamine andheated to effect hardening. The thermal property of the thus obtainedthermohardened resin is shown in Table 1.

EXAMPLE 9

The substantially same procedure as described in Example 5 was repeatedexcept that titanium tetrabuthoxide was employed in place of titaniumtetraisopropoxide. There was obtained a red, solid resin. The resin wasmixed with 10% by weight of hexamine and heated to effect hardening. Thethermal property of the thus obtained thermohardened resin is shown inTable 1.

EXAMPLE 10

The substantially same procedure as described in Example 7 was repeatedexcept that titanium tetrabuthoxide was employed in place of titaniumtetraisopropoxide. There was obtained a red, solid resin. The resin wasmixed with 10% by weight of hexamine and heated to effect hardening. Thethermal property of the thus obtained thermohardened resin is shown inTable 1.

EXAMPLE 11

The substantially same procedure as described in Example 8 was repeatedexcept that titanium tetrabuthoxide was employed in place of titaniumtetraisopropoxide. There was obtained a red, solid resin. The resin wasmixed with 10% by weight of hexamine and heated to effect hardening. Thethermal property of the thus obtained thermohardened resin is shown inTable 1.

EXAMPLE 12

The substantially same procedure as described in Example 1 was repeatedexcept that tetrapropoxysilane was employed in place oftetraethoxysilane. There was obtained a white, solid resin. The resinwas mixed with 10% by weight of hexamine and heated to effect hardening.The thermal property of the thus obtained thermohardened resin is shownin Table 1.

EXAMPLE 13

The substantially same procedure as described in Example 3 was repeatedexcept that tetrapropoxysilane was employed in place oftetraethoxysilane. There was obtained a white, solid resin. The resinwas mixed with 10% by weight of hexamine and heated to effect hardening.The thermal property of the thus obtained thermohardened resin is shownin Table 1.

EXAMPLE 14

The substantially same procedure as described in Example 1 was repeatedexcept that tetrabuthoxysilane was employed in place oftetraethoxysilane. There was obtained a white, solid resin. The resinwas mixed with 10% by weight of hexamine and heated to effect hardening.The thermal property of the thus obtained thermohardened resin is shownin Table 1.

EXAMPLE 15

The substantially same procedure as described in Example 3 was repeatedexcept that tetrabuthoxysilane was employed in place oftetraethoxysilane. There was obtained a white, solid resin. The resinwas mixed with 10% by weight of hexamine and heated to effect hardening.The thermal property of the thus obtained thermohardened resin is shownin Table 1.

EXAMPLE 16

282 g. of phenol, 90 g. of paraformaldehyde and 28 g. of water werecharged in a four-neck flask and heated, while stirring, to dissolve theparaformaldehyde, whereupon the temperature was lowered to 65°C. and0.282 g. (0.1% by weight based on the phenol) of p-toluenesulfonic acidwere added. The temperature was elevated to 90°C. and then, the reactionwas allowed to proceed at 90°C. for 60 minutes, followed by removal ofwater under a reduced pressure of 600 mmHg. At 90°C. in a 10% aqueoussolution of potassium hydroxide was added to adjust a pH value of thereaction system to 7.5 and water was completely removed, whereupon 28.4g. of titanium tetraisopropoxide were added and the temperature waselevated to 105°C. At that temperature the reaction was allowed toproceed for 60 minutes. Then, 31.2 g. of tetraethoxysilane were addedand the temperature was elevated to 130°C., whereupon the reaction wasallowed to proceed for 60 minutes, followed by concentration underreduced pressure to obtain a red, opaque, solid resin. The resin wasmixed with 10% by weight of hexamine and heated at 170°C. to effecthardening. The thermal property of the thus obtained thermohardenedresin is shown in Table 1.

COMPARATIVE EXAMPLE

245 g. of phenol and 165 g. of formalin were charged in a four-neckflask and 2 ml. of 1N HCl were added while stirring, whereupon thereaction was allowed to proceed at 95°C. for 120 minutes, followed byconcentration under reduced pressure to obtain a solid novolak. Thenovolak was mixed with 10% by weight of hexamine and heated to effecthardening. The thermal property of the thus obtained thermohardenedresin is shown in Table 1.

                  Table 1.                                                        ______________________________________                                        Result of Thermogravimetric Analysis                                          Temperature at which the resin is caused to show a weight                     loss of 6%*                                                                   ______________________________________                                        No. of   Temperature,  No. of     Temperature,                                Example  °C.    Example    °C.                                  ______________________________________                                        1        405           10         430                                         2        420           11         430                                         3        420           12         420                                         4        420           13         420                                         5        430           14         420                                         6        430           15         420                                         7        430           16         430                                         8        430                                                                                         Comparative                                            9        430           Example    280                                         ______________________________________                                         *20 mg. of the resin was taken as a specimen and the specimen was heated      at a temperature elevation rate of 10°C. per minute by employing a     Micro Electrobalance Type-8002 Thermogravimetric Analyser manufactured an     sold by Rigaku Denki Kabushiki Kaisha, Japan to determine the temperature     at which the resin was caused to show a weight loss of 6%.               

What is claimed is:
 1. A process for preparing a thermoset resin havinga thermal resistance such that the temperature at which the resin iscaused to show a weight loss of 6% when heated at a temperatureelevation rate of 10°C per minute is at least 400°C, said processcomprising the steps of reacting:1. a novolak obtained by the reactionof a phenol and an aldehyde in the presence of an acid catalyst with 2.a titanic acid ester of the formula Ti (OR)₄ wherein R represents alkylor aryl in the presence of an alkaline catalyst while keeping thereaction system in a molten state, said titanic acid ester beingemployed in an amount of 0.06-0.2 molar equivalents, based on the amountof phenol present in the starting system to be reacted with said titanicacid ester, to produce a thermosetting resin; addinghexamethylenetetramine to said thermosetting resin and heating theresultant mixture to produce the thermoset resin.
 2. A process forpreparing a thermoset resin according to claim 1 wherein said reactionsystem has a pH value of 7.5-10.0.
 3. A process according to claim 1wherein the reaction of said novolak resin with said titanic acid esteris carried out for a period of 20-150 minutes.
 4. A process according toclaim 1 wherein said phenol is a member selected from the groupconsisting of monohydroxybenzene, cresol,2,2-bis(p-hydroxyphenyl)-propane, and 2,6-bis-(2-hydroxybenzyl)phenol.5. A process according to claim 1 wherein said titanic acid ester is amember selected from the group consisting of titanium tetraisopropoxide,titanium tetrabuthoxide, tetra(2-ethyl)hexyl titanate, tetrastearyltitanate, titanyl acetylacetonato, and titanium tetraphenoxide.
 6. Aprocess according to claim 1 wherein said aldehyde is a member selectedfrom the group consisting of formaldehyde, acetaldehyde and furfural. 7.A thermoset resin prepared according to the process of claim
 1. 8. Athermoset resin prepared according to the process of claim
 4. 9. Athermoset resin prepared according to the process of claim
 5. 10. Athermoset resin prepared according to the process of claim 6.